S.L. Wolhart

Mapping Hydraulic Fracture Growth and Geometry Using Microseismic Events Detected by a Wireline Retrievable Accelerometer Array

Technology has advanced to the point where microseismic monitoring of hydraulic fractures can provide critical information for fracture optimization. Important elements of a monitoring system include the receivers, the telemetry system, and automatic processing of the vast amounts of data. Procedures and additional data requirements are discussed and examples of the important results which can be obtained are illustrated. Hydraulic fracturing is a critical technology for the exploitation of natural gas and oil resources, but its optimization has been impeded by an inability to observe how the fracture propagates and what its overall dimensions are. Recent field experiments in which fractures have been exposed through coring or mineback have demonstrated that hydraulic fractures are not the ideal, symmetric, planar features that are currently envisioned. Instead, they appear to commonly have multiple strands, secondary fractures, height and length asymmetries, and other complexities which make a priori predictions difficult. It is clear that model validation, fluid selection, proppant loadings, problem identification and solution, field development, and many other aspects of fracture optimization have been encumbered by the absence of ground-truth information on fracture behavior in normal field settings. Technology is now becoming available, however, to provide extensive diagnostic information on fracture growth, final size and geometry. Multi-level wireline receiver arrays for downhole passive imaging of fracture behavior have become viable and are demonstrating that hydraulic fractures can be imaged, assessed, and eventually controlled. These receiver arrays require high-quality transducers, well-designed clamping systems, high-speed telemetry, real-time processing capabilities, and careful procedures to be effectively used. This paper discusses this technology, its application and validation, and examples of the value of fracture imaging. It concentrates on a 5-level, accelerometer-based, fiber-optictelemetry system currently being used for microseismic mapping.

The Mounds Drill-Cuttings Injection Field Experiment: Final Results and Conclusions

This paper summarizes the results obtained from a comprehensive, joint-industry field experiment designed to improve the understanding of the mechanics and modeling of the processes involved in the downhole injection of drill cuttings. The project was executed in three phases: drilling of an injection well and two observation wells (Phase 1); conducting more than 20 intermittent cuttings-slurry injections into each of two disposal formations while imaging the created fractures with surface and downhole tiltmeters and downhole accelerometers (Phase 2); and verifying the imaged fracture geometry with comprehensive deviated-well (4) coring and logging programs through the hydraulically fractured intervals (Phase 3). Drill cuttings disposal by downhole injection is an economic and environmentally friendly solution for oil and gas operations under zero-discharge requirements. Disposal injections have been applied in several areas around the world and at significant depths where they will not interfere with surface and subsurface potable water sources. The critical issue associated with this technology is the assurance that the cuttings are permanently and safely isolated in a cost-effective manner. The paper presents results that show that intermittent injections (allowing the fracture to close between injections) create multiple fractures within a disposal domain of limited extent. The paper also includes the conclusions of the project and an operational approach to promote the creation of a cuttings disposal domain. The approach introduces fundamental changes in the design of disposal injections, which until recently was based upon the design assumption that a large, single storage fracture was created by cuttings injections.

Development of an Advanced Hydraulic Fracture Mapping System

The project to develop an advanced hydraulic fracture mapping system consisted of both hardware and analysis components in an effort to build, field, and analyze combined data from tiltmeter and microseismic arrays. The hardware sections of the project included: (1) the building of new tiltmeter housings with feedthroughs for use in conjunction with a microseismic array, (2) the development of a means to use separate telemetry systems for the tilt and microseismic arrays, and (3) the selection and fabrication of an accelerometer sensor system to improve signal-to-noise ratios. The analysis sections of the project included a joint inversion for analysis and interpretation of combined tiltmeter and microseismic data and improved methods for extracting slippage planes and other reservoir information from the microseisms. In addition, testing was performed at various steps in the process to assess the data quality and problems/issues that arose during various parts of the project. A prototype array was successfully tested and a full array is now being fabricated for industrial use.

Diffusion of Advanced Stimulation Technology in the Petroleum Industry: A Case History

The rate of technology diffusion or dissemination is controlled by many factors that are defined by both the innovation and the user or adopter. The decision to adopt an innovation is based on the perception of the innovation by the adopter.